This study proposes to prospectively monitor bone mass over a two year period in healthy women who are 10 or more years post- menopausal, and to relate the rate of bone loss to biochemical markers of bone remodelling measured at entry into the study. In a subset of the study population histologic assessment of bone remodelling will also be done at entry and related to the prospectively determined rate of bone loss. The methods of bone mass measurement (single and dual photon absorptiometry, quantitative densitometric radiography and quantitative computed tomography) permits evaluation of cortical and cancellous bone at different skeletal sites where osteoporotic fractures are common. The biochemical markers of bone remodelling include bone specific alkaline phosphatase, tartrate-resistant acid phosphatase and osteocalcin in the blood and urinary excretion of calcium and hydroxyproline. Additionally, in the subset having the bone biopsy, the short term response of these markers to calcitonin will be measured in an"effort to improve sensitivity and specificity. The principal objective of this study is to determine whether, in this age group, the rate of bone loss can be predicted when the patient first presents for evaluation. If such a prediction is possible it would form a rational basis for subsequent management decisions aimed at minimizing the risk of sustaining osteoporotic fractures later in life. These decisions would be made not only on the prevailing bone mass but on the predicted change in bone mass with time. This study could serve as a guide to the design of future clinical trials in this field.